MCP111 datasheet(11/32 Pages) MICROCHIP

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DS20001889F-page 11

MCP111/112

4.0

APPLICATION INFORMATION

For many of today’s microcontroller applications, care

must be taken to prevent low-power conditions that can

cause many different system problems. The most

common causes is a brown-out condition, where the

system supply drops below the operating level momen-

tarily. The second most common cause is when a slowly

decaying power supply causes the microcontroller to

begin executing instructions without sufficient voltage to

sustain SRAM, thus producing indeterminate results.

Figure 4-1 shows a typical application circuit.

FIGURE 4-1:

Typical Application Circuit.

4.1

TRIP Operation

The voltage trip point (V

TRIP) is determined on the falling

edge of V

DD. The actual voltage trip point (VTRIPAC) will

be between the minimum trip point (V

TRIPMIN) and the

maximum trip point (V

TRIPMAX). There is a hysteresis on

this trip point to remove any “jitter” that would occur on

the V

OUT pin when the device VDD is at the trip point.

Figure 4-2 shows the state of the V

OUT

pin as

determined by the V

DD voltage. The VTRIP specification

is for falling V

DD voltages. When the VDD voltage is

rising, the V

OUT pin will not be driven high until VDD is at

TRIP + VHYS.

FIGURE 4-2:

VOUT Operation as Determined by the VTRIP and VHYS.

4.2

Negative Going VDD Transients

The minimum pulse width (time) required to cause a

reset may be an important criteria in the implementa-

tion of a Power-on Reset (POR) circuit. This time is

referred to as transient duration, defined as the amount

of time needed for these supervisory devices to

respond to a drop in VDD. The transient duration time is

dependent on the magnitude of VTRIP – VDD. Generally

speaking, the transient duration decreases with

increases in VTRIP – VDD.

Figure 4-3 shows a typical transient duration vs. reset

comparator overdrive for which the MCP111/112 will

not generate a reset pulse. It shows that the farther

below the trip point the transient pulse goes, the

duration of the pulse required to cause a reset gets

shorter. Figure 2-18 shows the transient response

characteristics for the MCP111/112.

A 0.1 µF bypass capacitor, mounted as close as

possible to the VDD pin, provides additional transient

immunity (refer to Figure 4-1).

MCP11X

VDD

VOUT

MCLR

(Reset Input)

VSS

GND

PIC®

Microcontroller

RPU

Note 1: RPU may be required with the MCP111

due to the open-drain output. Resistor

RPU is not required with the MCP112.

0.1

µF

(1)

VDD

VTRIPMAX

VTRIPMIN

VTRIPAC

VTRIPAC + VHYSAC

VOUT

< 1 V is outside the

device specifications

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